Conventionally, such a circuit comprises means for comparing a reference signal with a first variable signal which is derived from the output voltage of the alternator, and for generating a first control signal having an electrical characteristic that varies as a function of the result of the comparison to cause the excitation of the alternator to vary.
Under such circumstances, when the vehicle engine is idling and the alternator is subjected to high current demand, as occurs particularly when switching on electrical equipment such as devices that use the Joule effect for de-icing or for heating, air conditioners, headlights, etc. . . , the voltage at the output from the alternator is caused to drop suddenly, thereby causing maximum excitation current to be applied thereto immediately. The torque load of the alternator on the engine therefore increases suddenly and that can cause the engine to hiccup or even to stall.
It is already known that the above drawback can be mitigated by ensuring that when the electrical load on the alternator increases suddenly, excitation of the alternator increases only progressively, in particular so as to allow time for an electronic engine control circuit to respond to the situation. Nevertheless, that kind of known circuit can be relatively complex and expensive to implement.
In addition, known circuits are generally active below a certain threshold number of engine revolutions per minute (rpm), and inactive above that threshold, and this often results in the regulator circuit behaving in a way that is poorly suited to the real revolution speed of the engine. In particular, progressive excitation of the alternator may take place even when that is unnecessary, thus giving rise to a period of time that is clearly perceptible to the driver during which the voltage of the electrical circuit of the vehicle is excessively low.